This invention relates generally to radiography. More particularly, the present invention relates to a device and method for measuring proportions of body materials in body parts of humans and animals.
The determination of proportions or densities of different body materials in body parts of humans or animals is of utmost importance to monitor, for instance, cancer risk in clinical drug trials, epidemiological studies, or routine screening. The measures of proportions or densities could be shown to be useful as markers to predict, for instance, breast cancer risk and possibly risk of disease recurrence or change in breast cancer risk.
In order to obtain these measures, techniques have been developed to maximize the radiographic contrast of tissue composition of a body part to better discriminate cancer risk. The x-ray energies, dose levels, and film/screen combinations are typically designed to maximize the radiographic tissue composition contrast. As an example, breast density was initially described using a semi-quantitative classification system that took into account the quantitative (amount of density) and qualitative nature of the density (diffuse or associated with ductal structures). Four to ten category systems have been previously used to cover the entire density range. A more quantitative approach measures the area of mammographically dense breast area relative to the total projected breast area, referred to as mammographic density. Mammographic density is a quantitative continuous grading from 0 to 100% density measured by delineating the radiographically dense areas in the mammogram from the entire breast area and providing a percentage breast density. Although mammographic density is currently a widely used technique, it has serious limitations. First, since the films are uncalibrated for mass density versus film optical density, a unique threshold has to be picked for each film. The total and dense projected areas will change based on the amount of compression. For example, in a typical laboratory, the reproducibility of delineating the dense regions by an expert radiologist on the same image is approximately 5-7%. If both delineation errors and patient repositioning errors are conservatively assumed to be 7%, the 95% confidence for a significant change in density is approximately 14%. Thus, the sensitivity for risk classification and change in follow-up examinations is similar to that of the categorical methods.
There are many competing methods readily available to estimate body fat but only a few, Dual Energy X-ray Absorptiometry (DXA), Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) are capable of measuring the tissue composition of specific compartments of the body. CT and MRI work by segmenting the fat from the lean tissue components for individual image planes. Summing all the slices of a whole breast scan to form a volume results in a whole organ % fat mass. The whole organ radiation dose of CT limits its usefulness as a screening tool. The overall costs and availability of both CT and MR further limit their practicality as a screening tool. For these reasons and its very high precision (xcx9c300 grams for human whole body measurements and  less than 50 g in small animals), DXA body composition measurements are the clinical standard for whole body and subregional compositional measurements. DXA measurements are low dose, typically less than 5 xcexcSv for any procedure, but require the acquisition of two images with beam hardening on the higher energy image. Prior to the development of DXA, Single Energy X-ray Absorptiometry (SXA) was used to measure bone density in peripheral bone site such as the forearm. For instance, a forearm was submerged in water such that the soft tissue in water provided uniform background attenuation. This technique eliminated the problem of soft tissue thickness variation and the bone attenuation was then simply the attenuation values above a water/soft tissue threshold.
Accordingly there is a need to develop a more practical device and method to quantify proportions or densities of different body materials in body parts of humans and animals.
This invention provides generally a radiography device and method. More particularly, the present invention provides a device and method for measuring proportions of body materials in body parts of humans and animals. The device and method enables one to determine a proportion of body materials in body parts of interest in, for instance, clinical drug trials and epidemiological cancer risk studies. Measures of body part proportions could be useful as a marker to predict cancer risk and possibly risk of disease recurrence or change in cancer risk. Furthermore, classification of cancer types could be improved with the device and method of the present invention since it provides for a more reproducible and more sensitive approach.
In accordance with exemplary embodiments of the present invention, a radiation device is provided for comparatively determining a proportion of body materials that define a body part. A more detailed embodiment is provided wherein breast density, as the proportion of body materials of a breast is determined. The present invention is, however, not restricted to the use of a breast and could also include other body parts of the human and animal body. The radiation device includes a device for retaining therein the body part in a uniform position. In addition, at least two reference materials that have attenuation characteristics are used. These reference materials are also retained in the retaining device. In the example of the breast, the reference materials represent for instance fat and lean tissue. However, the present invention is not limited to the choice of these materials or to the selection of only two materials. The breast could also be modeled as having three or more different materials. The reference materials are being positioned in the retaining device for the comparative determination during a simultaneous irradiation of the body part and the reference materials. The attenuation characteristics of the reference materials are selected in correspondence to the attenuation characteristics of the body materials in the body part. A radiation means for simultaneously irradiating the body part and the reference materials is used to create attenuated beams of the materials and the body part. A detector is used to detect and present the attenuated beams as attenuated values of the materials and the body part. A calculating means, such as a computer, is included for calculating the proportion of the body materials that define a particular body part of interest based on the attenuated values of the materials and the body part.
In view of that which is state above, it is the objective of the present invention to provide a device and method that determines a proportion of body materials as in for instance a fat and lean ratio of a breast. It is another objective of the present invention to provide a method and device to predict cancer risk and monitor drug trials. The advantage of the present invention is that the results obtained by using the device and method are irrespective of patient""s repositioning errors and reproducible. The device and method are also sensitive in determining the proportions of body materials. In addition, the device and method of the present invention does not require additional calibration. Finally, the present invention uses just one image of the body part of interest. This enables one to use radiation techniques such as single energy X-ray absorptiometry as well as single photon absorptiometry. Therefore an additional advantage is that the use of the present invention reduces the amount of radiation exposure.